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In our sessions we've recently discussed how a plant grows
in particular we've discussed primary and secondary growth the formation of different
stems and shoots and leaves and roots. And I've mentioned briefly what we mean
when we talk about plant hormones but
we haven't discussed in detail what a plant hormone is
in actuality
a plant hormone is no different than your hormones. They are chemical in nature and they cause particular
responses within plant cells. Specifically we look at hormones producing higher rates of cell division in particular
areas of the plant in response to some need of the plant -- so say in response to increase sunshine increased water availability
or just seasonally so changes in hormones as a response to changes in temperature and light availability
people start studying hormones because they observed odd behaviors in plants
we tease about plants not be able to run away from
the organisms that eat them, but we will look later on
at some very interesting responses to plants as they are chewed on! But these kinds of behaviors are what
made people start to think that there were chemicals controlling some of these responses
and trying to understand better what those chemicals actually were
phototropism - or a plants response to light - is actually what drove a lot of this
research just the very essence that a plant can bend towards the light
think about your houseplants at home or plants even outside
they tend to lean towards the light
and in any time lapse images you can see this occur on a daily basis. In the morning
if they're near sunny window
they will start to move towards the light of that window to absorb as much light is possible for photosynthesis
so scientists have spent
a lot of time trying to understand
how these different plant hormones work
But what I wanna focus on today is how those hormones actually affect plant growth in particular
So they are just simply chemical signals
Darwin who we often just associate with evolution spent many years studying plants
and in particular
spent a lot of time studying how plants move in response to their environment. With his son he conducted lots of experiments actually looking
at plant roots and shoots and how they were able to grow towards the light
they setup a number of different experiments if you are interested in looking them up
putting blocks in place
and literally they would cut the plants and put these
blocks of material in place and put the plants back together -- kind of miny plants surgery -- to
see whether or not they could effect the way the hormones moved
There are five different types of hormones that we look at in plant specifically -- auxins, cytokinins,
Gibberellins, ABA (abscisic acid) and ethylene
so ethylene may be one you've already heard of. We look at that primarily associated with ripening
of fruits but we'll look at it also as we look at aging of leaves and flowers and plants
It essentially makes things go in to -- in many cases a kind of rotting stage or very mature againg stage
The others will act as what we call agonistic hormones, or
antagonistichormones. we look at the auxins and cytokinins working together and then
we'll look at gibberellin and ABA as kind of working together and that'll be in more detail
in the next video